>"If you want to open a file, click twice on the icon for it." [AmIsmart]
It's worth noting that both 'click' and 'click on' are already shortened versions of the longer descriptions that were needed when the mouse and graphical interface were first introduced (and that are still needed for beginners). Readers familiar only with a command line interface would have no idea how a mouse worked or how clicking could select an item. Keeping the first clause "If you want to open a file...." (or better, "To open a file,..." -- we probably don't need to go into the reader's feelings about opening it :-), I'll make up what I imagine is the history of how this instruction has been written over the last few decades:
"Move the mouse until the cursor is over the icon and press the [left] mouse button twice rapidly."
Even there we're assuming that the reader knows what a cursor, icon, and mouse are.
A bit shorter:
"Move the cursor to the icon and double click."
That assumes that the reader knows that the mouse can used to move the cursor, that what you click is the [left] button on the mouse, and that 'double click' means not only 'click twice' but 'click twice rapidly'. Clicking twice slowly usually won't work.
Even shorter:
"Double click on the icon."
That assumes knowledge about moving the cursor and how to press the mouse button to select.
"Double click the icon."
Almost anybody who would understand 'double click on' would probably understand the more brief version too. I suspect this is why most technical writers prefer 'double click'. Google results:
"double click" 17,900,000
"double click on" 5,080,000
"click twice on" 44,300
It's worth noting that both 'click' and 'click on' are already shortened versions of the longer descriptions that were needed when the mouse and graphical interface were first introduced (and that are still needed for beginners). Readers familiar only with a command line interface would have no idea how a mouse worked or how clicking could select an item. Keeping the first clause "If you want to open a file...." (or better, "To open a file,..." -- we probably don't need to go into the reader's feelings about opening it :-), I'll make up what I imagine is the history of how this instruction has been written over the last few decades:
"Move the mouse until the cursor is over the icon and press the [left] mouse button twice rapidly."
Even there we're assuming that the reader knows what a cursor, icon, and mouse are.
A bit shorter:
"Move the cursor to the icon and double click."
That assumes that the reader knows that the mouse can used to move the cursor, that what you click is the [left] button on the mouse, and that 'double click' means not only 'click twice' but 'click twice rapidly'. Clicking twice slowly usually won't work.
Even shorter:
"Double click on the icon."
That assumes knowledge about moving the cursor and how to press the mouse button to select.
"Double click the icon."
Almost anybody who would understand 'double click on' would probably understand the more brief version too. I suspect this is why most technical writers prefer 'double click'. Google results:
"double click" 17,900,000
"double click on" 5,080,000
"click twice on" 44,300